The present invention pertains to a method for controlling or regulating a compressor or motor that can be switched on and off on demand, wherein a control unit that switches the compressor on and off is provided with the compressor. The invention also pertains to a compressor or motor that can be switched on and off on demand, wherein a control unit that switches the compressor on and off is provided with the compressor.
Some modern motor vehicles are equipped with a pneumatic rear suspension in order to maintain the height of the motor vehicle constant, independently of the motor vehicle load. If the motor vehicle needs to be raised after being loaded, the pneumatic springs are supplied with compressed air via a compressor. While the compressor is switched on, heat is developed in the compressor, leading to a temperature increase. If this temperature becomes excessively high, the compressor may be damaged. This is, in particular, the case if the motor vehicle is repeatedly subjected to heavy loads and the motor vehicle body is raised to the previous level with the aid of the pneumatic suspension. However, the compressor may also be damaged due to the improper utilization of the pneumatic suspension. Due to these circumstances, it is important to protect overheating of the compressor while it is switched on.
A compressor that can be switched on and off on demand is known from DE 196 21 946, wherein a control unit that switches the compressor on and off is provided with the compressor. The compressor is equipped with an overload protection means that protects it from overheating and functions as described below: while the compressor is switched on, the temperature in the compressor is estimated with the aid of the control unit based on the on-time of the compressor. The control unit switches off the compressor as soon as the estimated value exceeds an upper temperature threshold, above which the compressor may be damaged. Due to this measure, the compressor is able to cool off. An estimated value for the temperature in the compressor is also calculated in the control unit during the cooling-off phase. As soon as this estimated value falls short of a lower temperature threshold, the control unit switches the compressor on or allows the compressor to be switched on at a later time if the compressor is currently not needed.
The method for controlling or regulating a compressor that can be switched on and off on demand, which is known from DE 196 21 946 C1, can be carried out without temperature sensors because only estimated values for the temperature of the compressor are calculated in the control unit. In addition, the compressor of the pneumatic suspension is reliably protected from overheating, i.e., damage to the compressor is largely precluded, namely even if the pneumatic suspension is improperly actuated. However, it was determined that the upper temperature threshold is always reached or exceeded while the compressor is in use, i.e., the regulating process is interrupted by the control unit. This means that the regulating process is, if at all, only completed after a relatively long time delay, i.e., after the compressor has cooled off below the lower temperature threshold. Since the compressors of pneumatic suspension systems are, in most instances, well encapsulated for acoustic reasons and as protection from mechanical damage, the cooling-off time may last between a few minutes and 15 min. Such a long interruption or delay in the regulating process is unacceptable.
It is therefore an object of the present invention to develop a method for controlling or regulating a compressor or motor that can be switched on and off on demand, in which interruptions of the regulating processes are largely prevented.
Another object of the present invention is to develop a compressor or motor that can be switched on and off on demand, wherein a control unit that switches the compressor on and off is provided with the compressor that serves for carrying out the aforementioned method.